Research and Monitoring Report 2010

Transcription

1 Research and Monitoring Report 2010 CONTACT US Sea Turtle Conservation Bonaire Mabel Nava, Manager Phone: (+599) Cellular: (+599) HOTLINE: PO Box 492 Kralendijk, Bonaire Netherlands Antilles STCB is a member of Sea Turtle Conservation Bonaire Research & Monitoring Report 2010

2 TABLE OF CONTENTS WELCOME 1 NESTING BEACH MONITORING 2 FORAGING GROUND SURVEYS 5 SOMATIC GROWTH RATES 11 PRESENCE OF DISEASE 13 SATELLITE TRACKING 13 Appendix I. List of turtles captured and tagged during Appendix II. Lists of nests observed on Bonaire and Klein Bonaire during Appendix III. Funders and Donors during Appendix IV. Staff and Board of Directors 24 Appendix V. STCB partners, supporters and volunteers 25 Appendix VI. Ways to donate 27 Sea Turtle Conservation Bonaire Research & Monitoring Report 2010

3 We proudly present our 2010 Sea Turtle Research and Monitoring Report. Sea Turtle Conservation Bonaire is a non-governmental, non-profit, research and conservation organization that began in Our mission is to ensure the protection and recovery of Bonaire s sea turtle populations throughout their range. In 2010, we completed our 8th year of systematic research on the sea turtles of Bonaire. In this report you will read about the methods and results of our sea turtle research and monitoring activities, including nesting beach monitoring, foraging ground surveys, and turtle migration tracking. Four of the Wider Caribbean s six species of sea turtles are found in the waters of Bonaire. They are: the hawksbill (Eretmochelys imbracata), the green turtle, (Chelonia mydas), the loggerhead (Caretta caretta), and the leatherback (Dermochelys coriacea). The hawksbill and leatherback are considered critically endangered throughout their global ranges; and the green and loggerhead considered endangered. Bonaire offers a relatively safe haven for foraging juvenile hawksbill and green turtles, as well as critical nesting grounds for hawksbill, loggerhead, green, and the occasional leatherback. When STCB was founded in 1991, our sea turtles were threatened by direct harvest, accidental capture, and destruction of nests. Accordingly, our conservation efforts focused on direct protection for sea turtles. Now those threats are overshadowed by problems brought by increasing tourism and development. Using the information we gather in our research and monitoring activities, we are able to identify and implement proactive management and conservation actions to continue to protect Bonaire s sea turtles and their environments. We use our sea turtle conservation efforts also to encourage sustainable development and to emphasize a necessary balance between increasing tourism and development and the preservation of Bonaire s nature and environment. For more information about our conservation, education, and advocacy activities, please visit our website at: Our important work could not be completed without significant financial support. We would like to acknowledge our flagship funder, WWF-Netherlands and our major 2010 funders, the Dutch Caribbean Nature Alliance (DCNA), Pifworld and STCB-Netherlands. We are also thankful to our many other individual and business donors (Appendix III), to STCB staff and board members (Appendix IV), and the many business partners and volunteers that assisted us (see Appendix V). We especially would like to thank STINAPA-Bonaire for their continuing collaboration and support. Special thanks go to Gielmon Funchi Egbrechts who left STCB at the end of For eight years, Funchi served as a field specialist conducting turtle surveys, monitoring nesting, teaching Bonaire s youth about the importance of turtles to our island s environment, and acting as a goodwill ambassador for the organization. His work is greatly appreciated and we wish him well on his future path. Lastly, we would like to acknowledge Dr. Robert van Dam, our scientific advisor who oversees STCB s research efforts and helped substantially in the production of this report. We hope you find this report informative and that it encourages your interest and support for the sea turtles of Bonaire. Sea Turtle Conservation Bonaire Research & Monitoring Report

4 Nesting Beach Monitoring The beaches of Bonaire and Klein Bonaire were surveyed periodically for sea turtle nesting activity, with emphasis on the most actively used nesting area around "No Name" on Klein Bonaire. No Name beach received the best coverage as it is Bonaire s index beach for measuring annual fluctuations in nesting activity. Turtle nesting activity was first registered during 2010 on May 12 th, when a loggerhead nest was discovered at No Name beach. The first hawksbill nesting of the 2010 season also occurred at No Name on June 1 st, where also a very rare leatherback nest was laid on June 7 th was also a strong green turtle nesting year and the first nest for the species was found at Playa Chikitu on July 12 th. During 2010, a total of 5 loggerhead and 34 hawksbill nests were recorded on No Name beach, with May showing the greatest nesting activity for loggerheads, whereas hawksbills were most active in August (Figure 1). Figure 1. Temporal distribution of nests laid by loggerhead and hawksbill turtles at No Name beach, Klein Bonaire (top) and the beaches of Bonaire (bottom). Sea Turtle Conservation Bonaire Research & Monitoring Report

5 Figure 2. Diagram of individual hawksbill and loggerhead nest locations along No Name beach, Klein Bonaire. Yellow dots indicate beach markers. The visitor huts are located approximately at marker 600. Hawksbill nests at No Name were laid in clusters around the 300m and 1000m markers, whereas the few loggerhead nests were spread out along the most accessible and sandy sections of the beach (Figure 2). Figure 3 illustrates the 8-year trend in nesting activity for the three species most commonly encountered. For hawksbills and loggerheads, the trend indicates a stable to slight decline in the population. On the rest of Bonaire nesting activity by loggerhead and hawksbill turtles during 2010 occurred along the southwest coast (3 loggerhead and 4 hawksbill nests), Donkey beach (3 hawksbill nests) and at Boca Onima (1 hawksbill nest). Green turtle nesting in the Caribbean are known to fluctuate strongly in 2-3 year cycles and this also shows in the nesting activity for the species on Bonaire and 17 green turtle nests were encountered during 2010 (no nests were observed in 2009). Such annual fluctuations are typical for a population consisting of only a limited number of individuals. For all areas, the actual number of turtle nests deposited is probably slightly underestimated, as only nesting activity with confirmed egg presence (determined either shortly after laying or upon hatching) is counted. Sea Turtle Conservation Bonaire Research & Monitoring Report

6 Figure 3. Trend in nest numbers at No Name Beach, Klein Bonaire (solid lines) and totals for all Bonaire and Klein Bonaire nesting beaches (dashed lines). Nesting size and productivity were measured through nest revisions after hatching. Revision of 6 loggerhead nests, mostly at No Name Beach, yielded an average nest size of eggs (range ) and average hatching success for these nests was 76.2%. Revision of 36 hawksbill nests (29 nests at No Name beach, 7 at other locations) yielded an average nest size of eggs (range ) and hatching success of 74..8%. Both hawksbill and loggerhead hatching success rates were slightly higher than in 2009, indicating favorable nest incubation conditions on the beach at Klein Bonaire. The estimated number of hatchlings produced at the index beach of Klein Bonaire during 2010 can be calculated from the total number of nests, average nest size and average hatching rate. The 5 loggerhead and 34 hawksbill nests laid along No Name resulted in approximately 548 loggerhead and some 3670 live hawksbill hatchlings emerging from their nests. Whereas the number of hawksbill hatchlings emerging from No Name beach in 2010 remained stable, only about 1/3 as many loggerhead hatchlings emerged as compared to 2009, due to fewer nests deposited. Green turtles laid 17 nests during 2010, all but one at deposited on Playa Chikitu, Washington Park. The remaining nest was laid in coral rubble adjacent to the Fisherman s hut along the southwest coast of Bonaire. This nest fared poorly and only 7% of the eggs hatched. Revision of 15 green turtle nests at Playa Chikitu yielded an average nest size of eggs (range ) and a hatching success of 92.3%. An estimated 1800 green turtle hatchlings emerged from the Playa Chikitu nests. Sea Turtle Conservation Bonaire Research & Monitoring Report

7 Foraging Ground Surveys Foraging ground surveys were conducted by snorkeling along the entire west coast of Bonaire, circumnavigating Klein Bonaire, and in front of Lac Bay (figure 4, table 1). In addition, turtle surveys using the netting technique were performed inside Lac Bay. The purpose of these snorkeling surveys is to tag, sample, measure and photograph individual turtles, and to establish catch-per-unit-effort measures of turtle abundance. For comparison, the surveyed area was separated into sectors for comparison as follows: Klein Bonaire, Northwest and Southwest Bonaire, the reef outside of Lac Bay (Southeast), and inside Lac Bay itself. Figure 4. Sectors of coastal areas of Bonaire and Klein Bonaire covered during in-water surveys. Survey tracks are marked in gray (lines connect survey begin and endpoints, but do not necessarily indicate the precise survey tracks). Sea Turtle Conservation Bonaire Research & Monitoring Report

8 Table 1. In-water snorkeling survey effort in hours by sector from 2003 to From 2009 to 2010, green turtle abundance appeared to remain stable in all areas (figure 5), except on the reef outside of Lac Bay where a steady increase has been observed since 2006, which jumped in 2010 (figure 6). With the exception of the Lac Bay animals, the green turtles encountered during snorkeling surveys are mostly immatures smaller than 40 cm straight carapace length (SCL). Locations with particularly high green turtle abundance include Ebo s Reef at Klein Bonaire (associated with the sea grass beds in the shallow lagoon there), Playa Frans, and the Slagbaai area of Washington Park (figure 7). The reef in front of Lac Bay harbors a very high density of animals (for location see figure 9), which are associated with the Lac Bay sea grass pasture foraging grounds. Hawksbill turtles occur in lower numbers than green turtles throughout Bonaire and Klein Bonaire (figures 5 and 8) and their abundance in 2010, as compared to previous years, appeared to have dropped slightly in the surveyed areas. Similarly as for green turtles, but occurring in a much lower aggregation density but on average in greater body size (figure 10), immature hawksbill turtles are found on the reefs adjacent to Lac Bay, and these animals also use the bay for foraging. Other areas of relatively high hawksbill abundance are the east half of Klein Bonaire, Playa and the southwest tip of Bonaire. Figure 5. Comparison of catch-per-unit-effort survey results by sector around Klein Bonaire and Bonaire. Sea Turtle Conservation Bonaire Research & Monitoring Report

9 Figure 6. Comparison of catch-per-unit-effort survey results outside Lac on Bonaire s southeast coast. Figure 7. Locations where green turtles were captured during snorkeling surveys around Bonaire and Klein Bonaire. Sea Turtle Conservation Bonaire Research & Monitoring Report

10 Figure 8. Locations where hawksbills were captured during snorkeling surveys around Bonaire and Klein Bonaire. Netting surveys were conducted during two periods within Lac Bay: during May and December A total of 105 green turtles and 7 hawksbills were caught during these surveys. Figure 9 indicates the netting locations, aimed at areas with highest green turtle abundance as determined by observing turtles surfacing to breathe. Table 2 indicates the abundance trends for both species as measured by captures per hour of netting time ( net soak time ). Green turtles are vastly more abundant than hawksbills within Lac and their numbers appear to be stable or increasing slightly. Hawksbill abundance at Lac now appears to be stable, however their low catch rate by netting make it difficult to determine any true abundance trend. Sea Turtle Conservation Bonaire Research & Monitoring Report

11 Figure 9. Netting locations inside Lac Bay (white bars indicate net location and orientation), and locations of hand-captured green turtles (green circles) and hawksbills (red stars) on the reefs outside Lac Bay. Table 2. Comparison of catch-per-unit-effort results for netting surveys conducted at Lac Bay. Sea Turtle Conservation Bonaire Research & Monitoring Report

12 Figure 10. Size distribution of hawksbill and green turtles captured, tagged and measured at Bonaire. Black bars indicate recapture of turtles tagged in previous years. Combined, the snorkeling and netting surveys yielded a total of 188 individual green turtles and 43 hawksbills, of which 21 green turtles and 20 hawksbills were recaptures (Figure 10). An additional turtle, apparently an adult hybrid between hawksbill and loggerhead was caught briefly on April 21 st (figure 11), but the animal could not be tagged or measured. Sea Turtle Conservation Bonaire Research & Monitoring Report

13 Figure 11. Gielmon Egbreghts briefly holding an adult turtle, apparently a hawksbill-loggerhead hybrid. Gathering information on movement and somatic growth rates is possible by recaptures of previously tagged turtles. Our surveys detected one green turtle that had made a significant movement from their original capture location: immature green , first tagged at Sabadeco on February 11 th 2008, was recaptured in Lac Bay on May 6 th Juvenile hawksbill , tagged in 2006 at Washington Slagbaai, then recaptured at Playa Frans on 27 th February 2009, was twice recaptured in 2010: on December 10 th during a netting session and December 15 th during snorkeling surveys on the reef outside Lac. Recaptured turtles yielded substantial information on somatic growth rates for green turtles and hawksbills over a wide size range (Figure 12). For both species, animals caught in or near Lac Bay exhibited exceptionally high growth rates, suggesting that Lac Bay has very high quality foraging habitat. Growth rates of turtles living on the reefs along the rest of Bonaire and Klein Bonaire are more in line with those growth rates measured in other Caribbean turtle populations. Recaptured adult hawksbill turtles did not increase significantly in body size, which is normal in such animals. Figure 12. Somatic growth of hawksbill and green turtles recaptured at Bonaire, with turtles captured at Lac Bay indicated with open circles. Horizontal lines indicate the size range over which an individual s growth was recorded. Comparing the growth trajectories of two individual green turtles is further illustrative of the large habitat quality differences between foraging sites at Bonaire. In February and March 2007, two green turtles were tagged at Playa Frans, measuring 24.1 cm SCL and measuring 35.6 cm SCL. By November 2009, turtle had moved to Lac Bay where it was caught and measured, and Sea Turtle Conservation Bonaire Research & Monitoring Report

14 then again on May 10 th 2010, now measuring 46.0 cm SCL, an increase of 21.9 cm in little over 3 years. During the same period, turtle appears to have remained at Playa Frans, where the animal was recaptured on March 15 th 2010 measuring 39.7 cm SCL, an increase of 4.1 cm. The turtle that stayed at Playa Frans exhibits a growth rate only about 1/5 th the rate of the now Lac Bay resident green turtle , where immature green turtles have possibly the highest somatic growth rates measured for wild aggregations anywhere in the world. Figure 13. Comparison of juvenile green turtles both first captured at Playa Frans in Turtle (left) had moved to Lac Bay by 2009, whereas turtle (right) remains at Playa Frans. Turtle exhibited growth rates 5 times greater than that of turtle , indicating superior habitat quality for green turtles at Lac Bay. Recapture profiles also provide indications of the residency durations by species and habitat location (figure 14). Hawksbills appear to be more persistent than green turtles, and greenen turtles at Lac Bay remain longer in that habitat than elsewhere. Juvenile green turtles from areas other than Lac are mostly transient, remaining in place for up to two years unless they move to Lac Bay. Older and larger green turtles from Lac are probably underrepresented in the data due to our reduced ability to catch these powerful and fast-swimming animals. Figure 14. Distribution by year of initial tagging of recaptured turtles encountered during White-filled bars indicate turtles recaptured at Lac Bay, black bars for turtles elsewhere. Sea Turtle Conservation Bonaire Research & Monitoring Report

15 Presence of disease Fibropapillomatosis occurs in green turtles at Lac Bay and all animals captured there are examined for the presence of external tumors. None of the 133 green turtles examined during the two netting periods in 2010 exhibited evidence of obvious tumors. Several individuals did exhibit small wart-like skin irregularities, but these were not severe enough to be qualified as fibropapillomas. A few green turtles with obvious fibropapilloma tumors were seen during snorkeling surveys on the reef in front of Lac, but none of these animals were caught for detailed examination. The occurrence of fibropapillomatosis in the Lac Bay green turtles has declined and no longer affects as many individuals as observed in (Table 3). Table 3. Number of green turtles captured in Lac by survey period and occurrence of visible tumors. Satellite tracking Our satellite-tracking program continued to add to our knowledge of the migratory patterns and behavior of the adult sea turtles that come to Bonaire to mate and nest. After the nesting season, adult male and female sea turtles return to their resident foraging grounds. With satellite transmitters, we are able to learn where these turtles live outside of the nesting season and what routes are taken to return to those sites. Since our satellite-tracking program started in 2003, we have tracked 20 adult turtles as they returned to their resident foraging grounds. It is likely that these turtles were born on Bonaire many years ago, yet now live all around the Caribbean. From our tracking program, we know that our adult turtles can live as far as 2200 kilometers away and as close as Los Roques, only 150 kilometers to the east. During 2010, new Wildlife Computers model SPOT5 transmitters were placed on two nesting hawksbill turtles at Klein Bonaire and one green turtle at Playa Chikitu, Washington Park. The first turtle, a hawksbill named Valley, was encountered at No Name beach, Klein Bonaire, on September Sea Turtle Conservation Bonaire Research & Monitoring Report

16 3 rd and fitted with a SPOT5 transmitter. This hawksbill nested three more times, then departed to the north on October 14 th, swimming for 36 days to reach reefs northeast of Honduras (figure 15). The last transmission for this turtle was received on January 11 th 2011 indicating she remained on the same foraging grounds, about 1380 km from Klein Bonaire. Figure 15. Track of female hawksbill Valley from No Name beach, Klein Bonaire to a reef bank off the coast of Honduras. On September 20 th, a green turtle nesting at Playa Chikitu was fitted with a SPOT5 transmitter. This turtle was named Carice and she laid another nest on October 1 st, then departed towards the southeast and continued on to reach the Los Roques Archipelago on October 7 th 2010 (figure 16). The last transmission for Carice was received on January 23 rd 2011 from the same area, some 175 km from Bonaire. Figure 16. Track of female green turtle Carice from Playa Chikitu, Bonaire to Los Roques, Venezuela. Sea Turtle Conservation Bonaire Research & Monitoring Report

17 The last turtle of the season to be tracked was hawksbill Piffie, found nesting at No Name beach on October 7 th. The turtle departed Bonaire to the north around October 16 th, swimming to Puerto Rico and then on to Anegada Island, British Virgin Islands, arriving there on November 23 rd (figure 17). The turtle remains on a reef southeast of Anegada, about 840 km from Klein Bonaire, as of the latest transmission on March 6 th Figure 17. Track of female hawksbill Piffie from No Name beach, Klein Bonaire to Anegada, British Virgin Islands. Sea Turtle Conservation Bonaire Research & Monitoring Report

18 Appendix I. List of turtles captured and tagged during Green turtles Sea Turtle Conservation Bonaire Research & Monitoring Report

19 Green turtles (continued) Sea Turtle Conservation Bonaire Research & Monitoring Report

20 Green turtles (continued) Sea Turtle Conservation Bonaire Research & Monitoring Report

21 Green turtles (continued) Sea Turtle Conservation Bonaire Research & Monitoring Report

22 Hawksbill turtles Sea Turtle Conservation Bonaire Research & Monitoring Report

23 Appendix II. List of nests observed on Klein Bonaire during During 2010 a total of 5 loggerhead (Cc), 34 hawksbill (Ei), and one Leatherback (Dc) nest(s) were laid on the beaches of Klein Bonaire. Sea Turtle Conservation Bonaire Research & Monitoring Report

24 List of nests observed on other Bonaire beaches during During 2010 a total of 3 loggerhead (Cc), 8 hawksbill (Ei), and 17 green (Cm) turtle nests were laid on the beaches of Bonaire. Sea Turtle Conservation Bonaire Research & Monitoring Report

25 Appendix III Funders and Donors STCB is a non-profit, non-governmental organization. We raise funds through conservation and research grants, merchandise sales and from individual and business donors. Flagship Funder In 2008, WWF Netherlands expanded its longtime presence on Bonaire by awarding a 3-year grant in support of STCB s work in sea turtle conservation on Bonaire. This grant is administered by STINAPA Bonaire. Major Funders Dutch Caribbean Nature Alliance (DCNA) Pifworld Sea Turtle Conservation Bonaire Netherlands Platinum Donors Allerd Stikker Eco Dive Bonaire 2010 Marlene Robinson and Bruce Brabec Michael and Anne Contratto Astrid Kromhout and Henkjan Faber Maduro & Curiel s Bank (Bonaire) Gold Donors A+ Educators Woodwind Snorkel Sail Jan and Margreth Kloos Silver Donors Meade Lowance OBS de Pÿlstaart (School) Serena Black P.A. De Wit Bonnie and David Pascoe William Holman Patrick and Hettie Holian Lia Otterspeer Bronze Donors Leo Hoogenboom and Zsuzsanna Pusztai Anonymous contributors Sea Turtle Conservation Bonaire Research & Monitoring Report

26 Appendix IV Staff and Board(s) of Directors Staff Mabel Nava, Manager Funchi Egbrechts, Field Specialist Scientific Advisor Robert van Dam Intern Delphine Henkens, University of Louvain-la-Neuve (UCL), Belgium STCB Bonaire, Board of Directors Bruce Brabec, President/Treasurer Corine Gerharts Marlene Robinson Anouschka van de Ven Diana Sint Jago Albert de Soet, STCB Founder Guido Wiersma Advisory Members of the Board Jan Kloos Allerd Stikker STCB Netherlands, Board of Directors Pieter Borkent, Chair Marlene van Koert, Secretary Duco van Hogendorp, Treasurer Niels Valkering Albert de Soet, Advisor and STCB Founder Guido Wiersma Tom van Eijck, Advisor, first field project coordinator (1993) Sea Turtle Conservation Bonaire Research & Monitoring Report

27 Appendix V STCB Partners, Supporters and Volunteers International Partners Wider Caribbean Sea Turtle Conservation Network (WIDECAST) WWF Netherlands (WWF-NL) Support Bonaire, Inc. Regional Partners Dutch Caribbean Nature Alliance (DCNA) Nature Foundation St. Maarten Parke Nacional Arikok (Aruba) Saba Conservation Foundation St. Eustatius National Parks Foundation Turtugaruba Local Partners Bonaire Department of Environment and Natural Resources (DROB) CIEE Research Station Bonaire Jong Bonaire Progressive Environmental Solutions RCN Ministry of Economic Affairs, Agriculture and Innovation RCN Ministry of Infrastructure and Environment Salba Nos Lora STINAPA Bonaire Bonaire National Marine Park Washington-Slagbaai National Park Tene Boneiru Limpi Local Business Supporters These businesses provide ongoing support to STCB programs and activities through the donation of in-kind services: Administratiekantoor Brandaris BonPhoto Botterop Construction Bonaire Buddy Dive Resort Captain Don s Habitat Carib Inn (Bruce Bowker) CARGILL Salt Bonaire Harbour Village Marina Kantika di Amor Mangrove Kayak Center NetTech (Jake Richter & Susan Davis) SELIBON The Beach Shop at Harbour Village Wannadive Woodwind Snorkel Sail Sea Turtle Conservation Bonaire Research & Monitoring Report

28 2010 Volunteers Barbel Heusinkveld Breno Lobo Leanne Pinkerton Leo Hoogenboom Patrick and Hettie Holian Ralph Moogie Stewart Red Berger SGB students Tina Lindeken Anne Zaat Zsuzsanna Pusztai And to the many volunteers who helped with our in-water sea turtle surveys: Patrick, Hettie, John, Brenda, Alicia, Kelsey, Colleen, Zag, Laura, Luca, Maggie, Stan, Clive, Margo, Breno, Gregory, Ester, Del, Jose, Monique, Dee, Ramon, Diego, Agapito, Robert, Tina, Osha, Red, Patti, Bert, Brenda, Michelle, Leo, Mike, Linda, Marieke, Tom,Gigi Colleen, Zag, Nat, Sarah, Lotte, Felix, Dexo. Sea Turtle Conservation Bonaire Research & Monitoring Report

29 Appendix VI. Ways to donate You can help protect Bonaire s sea turtle populations by donating to STCB. We welcome and depend on the financial support of people like you. Whether it s $10, $100, or $10,000, whatever you give makes an important difference. Online: Go to our website at bonaireturtles.org Donate by mail: Make check payable to: Sea Turtle Conservation Bonaire And mail to: STCB PO Box 492, Kralendijk, Bonaire Netherlands Antilles Donate by bank transfer: To make a donation locally on Bonaire: Maduro & Curiel s Bank Bonaire Account name: Sea Turtle Conservation Bonaire Account number: To make a donation from the USA: Beneficiary: Sea Turtle Conservation Bonaire Account number: Beneficiary Bank: Maduro & Curiel s Bank Bonaire Swift code: MCBKANCUBON Correspondent Bank: Bank of America Swift Code: BOFAUS3N To make a donation from Europe: Beneficiary: Sea Turtle Conservation Bonaire Account number: Beneficiary Bank: Maduro & Curiel s Bank Bonaire Swift code: MCBKANCUBON Correspondent Bank for Euro: Rado Bank Nederland Swift Code RABONL2U To discuss other ideas for giving, please call Manager Mabel Nava at , or us at stcb@bonaireturtles.org Sea Turtle Conservation Bonaire Research & Monitoring Report